1. Field of the Invention
The present invention relates to a path multiplexing communication system, a communication node, and a communication method.
2. Description of the Related Art
When there are two or more paths available between two communication nodes, higher speed communication, compared to the case using single path, is possible since the bands of plural paths are multiplexed by load distribution of the traffic between both nodes among these paths. As techniques for multiplexing the bands of plural paths in a stable wired network, a round-robin system disclosed in Non-Patent Document 1 and a weighted round-robin system disclosed in Non-Patent Document 2 are known. A round-robin system is a technique to input data to each of paths in sequence, and a weighted round-robin system is a technique to decide the weight of load distribution depending on the difference of communication speeds among the plural paths. Further, as a technique for multiplexing the bands of plural paths including a more unstable wireless link, a Mobile Inverse Mux disclosed in Non-Patent Document 3 is known.
In these path multiplexing techniques, suppose that there is a node having path multiplexing function on a path to be multiplexed by other two nodes. In FIG. 8, nodes 1, 2, and 3 all have a path multiplexing function. In this case, if the node 1 communicates with the node 3, there is a path consisting of only link 13, which make it possible to communicate directly with each other. On the other hand, they can communicate with each other via a path consisting of link 11, node 2 and link 12. Multiplexing of these two path can be realized by configuring the node 2 to function as a mere relay node for the traffic between the nodes 1 and 3. Similarly, by configuring the node 1 to function as a mere relay node for the traffic between the nodes 2 and 3, the two paths between the nodes 2 and 3 are multiplexed. Thus, if there is a node having a path multiplexing function on a path to be multiplexed, by configuring each node to act according to the traffic, it is possible to share part of the paths to be multiplexed among different nodes, and hence to improve the efficiency of utilization of network resources.    [Non-Patent Document 1] “Striping Within the Network Subsystem,” IEEE Network, July/August 1995.    [Non-Patent Document 2] M. Katevenis, S. Sidiropoulos, C. Courcoubetis, “Weighted Round-robin Cell Multiplexing in a General-Purpose ATM Switch Chip,” IEEE Journal on Selected Areas in Communications, Vol. 9, Issue 8, pp. 1265-1279 (October 1991).    [Non-Patent Document 3] T. Nakata et al., “Efficient Bundling of Heterogeneous Radio Resources for Broadband Internet Access from Moving Vehicles,” Proceedings of Global Mobile Congress 2004, Oct. 11-13 2004, Shanghai, China.    [Non-Patent Document 4] Dovrolis, Ramanathan, and Moore, “What Do Packet Dispersion Techniques Measure?” IEEE INFOCOM 2001.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-320420.
Suppose that traffic is given to both the node 1 and the node 2 to be transmitted to the node 3 at an instant. If both nodes transmit traffic to the node 3 using plural paths, they need to have a path multiplexing function in addition to a relay function. For the sake of simplicity, it is assumed that the link 11 has a wider band than the other links. For example, if the node 1 communicates with the node 3 via the node 2, the link 12 is a bottleneck on the path. Here, if a fixed weighting information is given to node 1 as shown in Non-Patent Document 2 or load distribution is performed by node 1 based on the bandwidth estimation result as shown in Non-Patent Document 3, each according to the bandwidth of the link 12 and the link 13 which can form a path for direct communication, since traffic between the nodes 2 and 3 also exists on the link 12, an actually available bandwidth of the link 12 for communication between node 1 and node 3 is narrower than the case where there is no such traffic sharing link 12.
Since Non-Patent Document 2 and Non-Patent Document 3 do not consider the existence of traffic among nodes as mentioned above, they cannot perform optimum load distribution. In general, as shown in Non-Patent Document 4, it is difficult to estimate an available bandwidth by the method using packet dispersion, disclosed in Non-Patent Document 3, if traffic exists in a section other than the section between endpoints to be measured, which is called ‘cross traffic’, when the bandwidth of a path is estimated only at the endpoint of one path.
The above-mentioned problem does not arise if each traffic rate is low enough not to cause congestion in each of the links, when the nodes 1 and 2 perform load distribution to both the links 13 and 12. Since the traffic between the node 1 and 3 and the traffic between the nodes 2 and 3 are both low rates, the deficiency of bandwidth does not occur even without load distribution to the plurality of paths. However, the bandwidth of the link 11, included only in the paths which use node 1 or 2 as a relay node, is consumed although the bandwidth is unnecessary for the purposes of bandwidth supply between the nodes 1 and 3 and bandwidth supply between the nodes 2 and 3.
On the other hand, Patent Document 1 discloses other technique for load distribution, which is realized by calculating load based on collected traffic characteristics information and by determining whether a transmission path should be added or deleted based on the calculated load.
However, by the technique disclosed in Patent Document 1, the amount of communication data among each of nodes becomes large since traffic characteristics information themselves are transmitted/received among each of nodes for collecting information. Here, for example, parameters like queue length and the number of flows can be such traffic characteristics. However, if these variables are transmitted/received among all of the nodes, the amount of data can become enormous as the number of nodes increases. Flexibility in determining whether a transmission path should be added or deleted also can be a problem. Further, if information on other than traffic, such as, for example, the reliability of the path, the possibility of a cyberattack, or the degree of battery drain (if it is a mobile node) should be considered as a criterion, not only does the protocol become complicated, but also does the amount of communication increase according to the number of criteria by the technique described in Patent Document 1 since communication among each of nodes has to be defined corresponding to all the criteria. Further, as the technique described in Patent Document 1 requires that each node collects and transmits only the status and all of the determination are conducted by a transmitting node, there is a problem that calculation load for determination is concentrated on the transmitting node.